1. Field of the Disclosure
The invention generally relates to wireless communication systems and, more particularly, to wireless communications based on RF transmissions from microdischarge-based devices.
2. Brief Description of Related Technology
Many sensor applications involve the deployment of a sensor or sensing device in biohazardous or other harsh conditions. Such conditions may, for instance, call for the detection of a harmful chemical species in gaseous form. Gas or vapor sensors often utilize a discharge pulse for excitation of a gaseous species to generate characteristic light emissions in the UV or visible range. One recent type of vapor sensor is described in B. Mitra, et al., “A low-power, three-terminal device for high speed detection of vapors at atmospheric pressure,” IEEE MEMS (January 2005). With these sensors, detecting the presence of a certain chemical species in the ambient often involves analyzing an optical spectrum of an emission.
Another type of harsh condition or environment to be monitored involves the detection of radioactive chemicals or other sources of radiation. In this case, a sensing device, such as a Geiger counter, can detect their presence by counting each discharge pulse resulting from the ionization of a trapped gas by an incoming particle. A number of such discharge-based sensors have been constructed using solid-state technology to detect the various types of radiation. One recently developed microfabricated Geiger counter has separate cavities to differentiate between beta particles of differing energies, thereby providing a manner in which to identify different radioactive sources. See C. G. Wilson, et al., “A microfabricated beta-particle detector with dual cavities for energy spectroscopy,” IEEE MEMS (January 2005).
The deployment of these and other sensing devices may often require wireless transmission of the data gathered by the device, especially in applications involving harsh or unfavorable environments. More generally, advances in wireless sensor communications have been useful in applications requiring a network of sensors widely distributed in conditions where wired connections are impracticable or impossible. Communication standards such as Bluetooth and IEEE 802.15.4 (i.e., Zigbee) have been used and established to support such sensor networks and sensor communications. These standards define signal transmission protocols for narrow band RF communications in, for instance, the dedicated ISM band, around 2.4 GHz.
Despite the advances made to support such wireless sensor communications, the transmitter electronics required for each sensor device can act as an application limiting factor in a number of ways, including cost, size, power consumption and, thus, operational lifetime. The transmitter, antenna, and other components necessary for wireless communication may collectively constitute the most expensive and sizeable module of a device having a microfabricated sensor. A potentially greater limitation on sensor deployment, however, may involve the amount of power dissipated by the transmitter, which alone may render certain sensing applications infeasible. For example, an IEEE 802.15.4 transmitter in the 2.4 GHz band may consume about 20-30 mW of active power during transmission. As a result, applications requiring considerable power to support, for instance, long sensor operational lifetimes or frequent data transmissions will need to accommodate large batteries or other cumbersome power sources to support the wireless communications. Unfortunately, in many cases, large batteries are incompatible with other aspects of the sensing device or unsuitable for the sensing application.